A GSM modem is a cellular communication device that connects software or hardware to a mobile network so it can send and sometimes receive SMS messages. In industrial and monitoring systems, it often acts as a notification bridge: an application sends a command to the modem, and the modem delivers the text message over the carrier network.
In cyber security, GSM modems matter because they sit on a trust boundary. If an exposed web or command interface can control the modem without authentication, an attacker may be able to trigger fake alerts, flood operators with SMS traffic, or misuse the device as an outbound communication channel. Defenders should treat modem-backed messaging as privileged functionality, restrict access to the management interface, log unusual SMS activity, and disable the feature when it is not needed.